Ultralow-threshold Raman laser using a spherical dielectric microcavity


The ability to confine and store optical energy in small volumes has implications in fields ranging from cavity quantum electrodynamics to photonics. Of all cavity geometries, micrometre-sized dielectric spherical resonators are the best in terms of their ability to store energy for long periods of time within small volumes1. In the sphere, light orbits near the surface, where long confinement times (high Q) effectively wrap a large interaction distance into a tiny volume. This characteristic makes such resonators uniquely suited for studies of nonlinear coupling of light with matter. Early work2,3 recognized these attributes through Raman excitation in microdroplets—but microdroplets have not been used in practical applications. Here we demonstrate a micrometre-scale, nonlinear Raman source that has a highly efficient pump–signal conversion (higher than 35%) and pump thresholds nearly 1,000 times lower than shown before. This represents a route to compact, ultralow-threshold sources for numerous wavelength bands that are usually difficult to access. Equally important, this system can provide a compact and simple building block for studying nonlinear optical effects and the quantum aspects of light.

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Figure 1: Cascading multiple Raman lasers along a single fibre.
Figure 2: Spectrum of a 70-µm-diameter Raman microsphere laser with pump powers of 2 mW.
Figure 3: Coupling gap and size dependence of the Raman threshold.
Figure 4: Single longitudinal mode Raman lasing.


  1. 1

    Collot, L., Lefevre-Seguin, V., Brune, M., Raimond, J. M. & Haroche, S. Very high-Q whispering-gallery mode resonances observed on fused silica microspheres. Europhys. Lett. 23, 327–334 (1993).

    ADS  CAS  Article  Google Scholar 

  2. 2

    Qian, S. X. & Chang, R. K. Multiorder Stokes emission from micrometer-size droplets. Phys. Rev. Lett. 56, 926–929 (1986).

    ADS  CAS  Article  Google Scholar 

  3. 3

    Lin, H. B., Huston, A. L., Eversole, J. D. & Campillo, A. J. Double-resonance stimulated Raman-scattering in micrometer-sized droplets. J. Opt. Soc. Am. B 7, 2079–2089 (1990).

    ADS  CAS  Article  Google Scholar 

  4. 4

    Braunstein, D., Khazanov, A. M., Koganov, G. A. & Shuker, R. Lowering of threshold conditions for nonlinear effects in a microsphere. Phys. Rev. A 53, 3565–3572 (1996).

    ADS  CAS  Article  Google Scholar 

  5. 5

    Knight, J. C., Cheung, G., Jacques, F. & Birks, T. A. Phase-matched excitation of whispering-gallery-mode resonances by a fiber taper. Opt. Lett. 22, 1129–1131 (1997).

    ADS  CAS  Article  Google Scholar 

  6. 6

    Chang, R. K. & Campillo, A. J. (eds) Optical Processes in Microcavities (World Scientific, Singapore, 1996).

    Google Scholar 

  7. 7

    Gorodetsky, M. L., Savchenkov, A. A. & Ilchenko, V. S. Ultimate Q of optical microsphere resonators. Opt. Lett. 21, 453–455 (1996).

    ADS  CAS  Article  Google Scholar 

  8. 8

    Weiss, D. S. et al. Splitting of high-Q Mie modes induced by light backscattering in silica microspheres. Opt. Lett. 20, 1835–1837 (1995).

    ADS  CAS  Article  Google Scholar 

  9. 9

    Lai, H. M., Leung, P. T., Young, K., Barber, P. W. & Hill, S. C. Time-independent perturbation for leaking electromagnetic modes in open systems with application to resonances in microdroplets. Phys. Rev. A 41, 5187–5198 (1990).

    ADS  CAS  Article  Google Scholar 

  10. 10

    Zhang, J. Z. & Chang, R. K. Generation and suppression of stimulated Brillouin scattering in single liquid droplets. J. Opt. Soc. Am. B 6, 151–153 (1989).

    ADS  Article  Google Scholar 

  11. 11

    Cai, M., Painter, O. & Vahala, K. J. Observation of critical coupling in a fiber taper to a silica-microsphere whispering-gallery mode system. Phys. Rev. Lett. 85, 74–77 (2000).

    ADS  CAS  Article  Google Scholar 

  12. 12

    Lin, H. B. & Campillo, A. J. CW nonlinear optics in droplet microcavities displaying enhanced gain. Phys. Rev. Lett. 73, 2440–2443 (1994).

    ADS  CAS  Article  Google Scholar 

  13. 13

    Ilchenko, V. S. & Gorodetskii, M. L. Thermal nonlinear effects in optical whispering gallery microresonators. Laser Phys. 2, 1004–1009 (1992).

    Google Scholar 

  14. 14

    Vernooy, D. W., Ilchenko, V. S., Mabuchi, H., Steed, E. W. & Kimble, H. J. High-Q measurements of fused-silica microspheres in the near infrared. Opt. Lett. 23, 247–249 (1998).

    ADS  CAS  Article  Google Scholar 

  15. 15

    Bachor, H.-A., Levenson, M. D., Walls, D. F., Perlmutter, S. H. & Shelby, R. M. Quantum nondemolition measurements in an optical-fiber ring resonator. Phys. Rev. A 38, 180–190 (1988).

    ADS  CAS  Article  Google Scholar 

  16. 16

    Silberhorn, Ch. et al. Generation of continuous variable Einstein-Podolsky-Rosen entanglement via the Kerr nonlinearity in an optical fiber. Phys. Rev. Lett. 6, 4267–4270 (2001).

    ADS  Article  Google Scholar 

  17. 17

    Treussart, F. et al. Evidence of the intrinsic Kerr bistability of high-Q microsphere resonators in superfluid helium. Eur. Phys. J. D 1, 235–238 (1998).

    ADS  CAS  Article  Google Scholar 

  18. 18

    Fan, X., Palinginis, P., Lacey, S., Wang, H. & Lonergan, M. C. Coupling semiconductor nanocrystals to a fused-silica microsphere: a quantum-dot microcavity with extremely high Q factors. Opt. Lett. 25, 1600–1602 (2000).

    ADS  CAS  Article  Google Scholar 

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We thank A. D. Stone and R. K. Chang for comments. This work was supported by DARPA, NSF and the Caltech Lee Center.

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Correspondence to K. J. Vahala.

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Spillane, S., Kippenberg, T. & Vahala, K. Ultralow-threshold Raman laser using a spherical dielectric microcavity. Nature 415, 621–623 (2002). https://doi.org/10.1038/415621a

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